Our current research is focused on two different but related problems: 1) that of stimulation-produced analgesia from brain stem electrical stimulation in the rat; and 2) that of the normal physiological circumstances calling into action the brain's own pain-inhibitory systems. Within each of these domains we have recent evidence for the coexistence of opioid and nonopioid systems. Our studies of these mechanisms are continuing with the application of both biochemical and electrophysiological techniques to supplement the behavioral and pharmacological approaches already taken.